热水袋的保养方法是将袋内水倒尽、倒挂、晾干后旋紧塞子，存放于阴凉处备用。
参考答案：错
It suddenly occurred to him _____ he had left his keys in the office.
A．whether
B．where
C．which
D．that
随着尿素含量的增大，甲铵的熔点（）。
